1. Field of the Invention
The present invention relates to an information recording medium comprising at least two recording layers, a method and apparatus for recording information onto this medium, and a method and apparatus for reproducing information from this medium.
2. Description of the Related Art
In recent years, various information recording media capable of recording/reproducing a large volume of information have been developed. Among them are optical discs. One of large-capacity optical discs is a double-sided optical disc comprising two optical discs attached together, on each of which information can be recorded/reproduced. However, there is a demand for a high-capacity, but single-sided and random access disc which is unnecessary to be turned upside down, for some applications, such as computers, games, and the like, in which random accesses are frequently required.
To meet such a demand (high-capacity, random access, and single-sided), it is conceivable that a single optical disc comprises at least two recording layers (such an optical disc may be referred to be a multi-layer optical disc), where information can be recorded/reproduced on a single side thereof. FIG. 7 shows a configuration of an optical disc 700 comprising two recording layers on one side thereof.
The optical disc 700 comprises a first recording layer 704, a first substrate 705, an adhesive resin 703, a second substrate 701, and a second recording layer 702. Each substrate is provided with a clamp hole 706. The second recording layer 702 comprises a disc information area 707 and a data area 710. The first recording layer 704 comprises a disc information area 711 and a data area 714.
The first substrate 705 and the second substrate 701 are made of polycarbonate resin or the like and are used to protect the first recording layer 704 and the second recording layer 702, respectively. The disc information area 707 is a reproduction-only area in which information, such as the power of laser light to irradiate the second recording layer 702 and the like. The disc information area 711 is also a reproduction-only area in which information, such as the power of laser light to irradiate the first recording layer 704, and the like.
In the optical disc 700, for example, reproduction is first performed on the first recording layer 704, immediately followed by reproduction on the second recording layer 702. In this case, reproduction operations are performed in the following order: information indicating the power of laser light for irradiating the first recording layer 704 is reproduced from the disc information area 711; reproduction is performed on the data area 714; information indicating the power of laser light for irradiating the second recording layer 702 is reproduced from the disc information area 707; and reproduction is performed on the data area 710. Alternatively, reproduction operations are performed on the disc information area 711, the disc information area 707, the data area 714, and the data area 710 in this order. Thus, in the optical disc 700, information has to be reproduced from two disc information areas. Therefore, it takes a long time to reproduce information of the parameters and formats of the optical disc 700, such as the power of laser light and the like.